The present invention relates generally to an apparatus and method for locating an electrode position, and more particularly, is directed to an apparatus and method for locating and mapping a catheter for use in intracardiac applications such as cardiac arrhythmia, ventricular tachycardia and other heart disorders.
Cardiac arrhythmia, which is an irregular heartbeat, is the leading cause of death in the United States. For example, ventricular tachycardia (VT), which is an excessively fast heartbeat, that is, a very rapid contraction of the heart muscle, is the cause death of about 300,000 patients annually. Therefore, it is necessary to detect defects in the heart rhythm, and locate the position of the these defects.
Generally, with regard to the heart pulses, there is an electrical signal that travels down the inner walls of the heart, contracting the heart from the top to the bottom in much like a squeezing action. As the electrical signal passes vertically along the inner walls of the heart to produce the contraction, the heart then expands again. At the end of the signal, that is, at the bottom of the heart, the signal has ended and a new signal starts at the top of the heart to again begin contraction.
However, oftentimes, there are dead or defective tissue or small lesions on the inner walls of the heart. In such case, the small lesions disturb the conduction of the electrical pulse. This results in delay of the pulse to reach the bottom of the heart and to be entirely canceled out. As a result, an extra pulse is produced which causes the heart to pre-contract again before it should, resulting in a double pulse, or double contraction, causing ventricular tachycardia (VT) or an excessively fast heartbeat. Since a full heart pump is not produced for each pulse, this causes problems in getting the necessary blood flow to all parts of the body.
In order to cure this problem, the defective tissue or small lesions of the heart wall are burned out or ablated. As a result, the burned out areas are bypassed by the electrical signal that travels down the heart wall, so that no double pulse or double contraction is produced, and a regular heartbeat is achieved.
In order to detect this defective tissue of the heart, catheters are conventionally inserted through main blood vessels into the inside of the heart. The catheters have spaced metal contacts on the outside thereof which touch the inner wall of the heart at different locations. When the catheter touches the inner wall of the heart, it detects the signals which stimulate the contraction and which run along the heart. Alternatively, stimulus signals can be supplied to the heart, and be detected by the catheter electrodes. A plurality of such catheters can be provided for such measurement in the heart at one time.
Conventionally, however, this process has proved to be time-consuming, and burdensome with difficulties to locate the electrode position in relation to the heart interior. The procedure for locating the defective tissues utilizes electro-physiology examination that provides mapping by electrical activity of the heart. Specifically, this procedure requires constant movement of the sensing electrodes, combined with x-ray illumination needed for gathering positioning reference points. Such procedure is tedious, time-consuming, and requires constant use of x-ray illumination for imaging and mapping, exposing the patient and physician to high doses of harmful radiation.
Further, locating the position of a catheter inserted into body organs, and in particular, sensitive organs such as the heart, is considered a difficult procedure. The only effective method today is the use of x-ray illumination, as discussed above. However, the x-ray illuminations usually result in poor or fuzzy imaging due to the fact that x-ray does not produce good image of soft tissue in comparison to hard tissue such as bones. Therefore, this procedure results in a poor image of the heart anatomy. In intracardiac mapping applications where accurate positioning of the inserted electrode is important, x-rays therefore do not provide absolute positioning in respect to the heart interior walls.
After mapping the position of the defective tissue or small lesions of the heart, a separate ablation catheter is inserted into the heart and includes a heating element to burn out the defective tissue. Because it is impossible with the use of x-rays to determine the exact location of the defective tissue, the ablation catheter is used to burn out an area which is much larger than each area of defective tissue, in order to ensure that all of the defective tissue is burned out.
This procedure causes problems, because there are key nerves lining the heart, and it is not known from the mere use of the above sensing electrodes if one of the key nerves is being burned out. If it is burned out, the patient may thereafter require a pacemaker.
Thus, with this prior procedure using x-rays, there is no way to determine the exact location of the sensing electrodes or catheters, and there is no way to document previous positions of the catheters. Further, this procedure is long and tedious, and subjects the patient to long use of x-rays, as discussed above.
A summary of this known system and the disadvantages thereof are found at columns 1 and 2 of the U.S. Pat. No. 5,480,422 to Ben-Haim.